Salts of onium or transition metal complex are known in prior art as cationic polymerization initiators for curing cationic polymerizable compounds, such as, epoxy compounds by heat or irradiation with active energy beams, such as, by light and electron beam (refer to Patent Reference 1).
In addition, as these salts of onium or transition metal complex produce acids by heat or irradiation with active energy beams are also referred to as acid generators and used in resists and photosensitive materials (refer to Patent Reference 2).
Incidentally, the cationic polymerization initiators described in these specifications contain BF4−, PF6−, AsF6− and SbF6− as anions, cation polymerization initiation capability differs depending on the species of the anion, improving in the order BF4−<PF6−<AsF6−<SbF6−. However, applications using the cationic polymerization initiators containing AsF6− and SbF6−, which have good polymerization initiation capability, are limited due to the problem of toxicity of As and Sb, such that only SbF6− salts are used in limited applications, such as, stereolithography. Therefore, PF6− salts, which have poor polymerization initiation capability, are generally used; however, for instance, in order to obtain a curing speed that is on the same order as that of SbF6− salts, the addition of nearly 10 times the quantity of the latter is required for PF6− salts, and problems exist, such as, loss of physical properties of the cured material due to the large residual amounts of unreacted initiator, solvent used as necessary to dissolve the initiator or decomposition products from the initiator, furthermore, easy corrosion of substrates, equipments and the like due to large amounts of the byproduct HF from the decomposition of the initiator. Therefore, a cationic polymerization initiator not containing a toxic element, having a cationic polymerization initiation capability that is comparable to that of SbF6− salts, is strongly sought.
Onium salts or salts of transition metal complex having tetrakis (pentafluorophenyl) borate as anion are proposed as cationic polymerization initiators responding to this problem (refer to Patent Reference 3); however, although the polymerization initiation capability thereof with respect to cationic polymerizable compounds is better than that of those having PF6− as anion, it is poorer compared to that of those having SbF6− as anion, such that an still better improvement is desired.
[Patent Reference 1] Japanese Patent Application Laid-Open No. S50-151997, Japanese Patent Application Laid-Open No. S50-158680, Japanese Patent Application Laid-Open No. H2-178303, U.S. Pat. No. 4,069,054, idem 4450360, idem 4576999, idem 4640967, Canadian Patent No. 1274646, European Patent Application Disclosure No. 203829
[Patent Reference 2] Japanese Patent Application Laid-Open Nos. H2002-193925, 2001-354669, 2001-294570
[Patent Reference 3] Japanese Patent Application Laid-Open No. H6-184170